eMedicine Specialties > Emergency Medicine > Obstetrics & Gynecology
Placenta Previa
Updated: Aug 10, 2009
Introduction
Background
Placenta previa is an obstetric complication that occurs in the second and third trimesters of pregnancy. It may cause serious morbidity and mortality to both the fetus and the mother. It is one of the leading causes of vaginal bleeding in the second and third trimesters.
Placenta previa.
Placenta previa is generally defined as the implantation of the placenta over or near the internal os of the cervix.
- Total placenta previa occurs when the internal cervical os is completely covered by the placenta.
- Partial placenta previa occurs when the internal os is partially covered by the placenta.
- Marginal placenta previa occurs when the placenta is at the margin of the internal os.
- Low-lying placenta previa occurs when the placenta is implanted in the lower uterine segment. In this variation, the edge of the placenta is near the internal os but does not reach it.
- A recent study concluded that more than two thirds of women with a distance of more than 10 mm from the placental edge to cervical os have vaginal delivery without an increased risk of hemorrhage.1
Pathophysiology
The exact etiology of placenta previa is unknown. The condition may be multifactorial and is postulated to be related to multiparity, multiple gestations, advanced maternal age, previous cesarean delivery,2 previous abortion, and possibly, smoking. Unlike first trimester bleeding, second and third trimester bleeding is usually secondary to abnormal placental implantation.
Frequency
United States
Placenta previa complicates approximately 5 of 1,000 deliveries and has a mortality rate of 0.03%. Data recorded from 1989-1997 indicated placenta previa occurs in 2.8 per 1000 live births in the United States.
Mortality/Morbidity
The maternal mortality rate secondary to placenta previa is approximately 0.03%. Babies born to women with placenta previa tend to weigh less than babies born to women without placenta previa. The risk of neonatal mortality is higher for placenta previa babies compared with pregnancies without placenta previa. The great majority of deaths are related to uterine bleeding and the complication of disseminated intravascular coagulopathy. In early pregnancy, a partial previa can often self-correct as the uterus enlarges and the placental site moves cephalad.
Race
Significance of race is somewhat controversial. Some studies suggest an increased risk of placenta previa among blacks and Asians, whereas other studies cite no difference.
Age
Women older than 30 years are 3 times more likely to have placenta previa than women younger than 20 years.
Clinical
History
Placenta previa is one of the leading causes of vaginal bleeding.
- Vaginal bleeding is apt to occur suddenly during the third trimester.
- Bleeding is usually bright red and painless. Some degree of uterine irritability is present in about 20% of the cases.
- Initial bleeding is not usually profuse enough to cause death; it spontaneously ceases, only to recur later.
- The first bleed occurs (on average) at 27-32 weeks' gestation.
- Contractions may or may not occur simultaneously with the bleeding.
Physical
- Profuse hemorrhage
- Hypotension
- Tachycardia
- Soft and nontender uterus
- Normal fetal heart tones (usually)
- Vaginal and rectal examinations
- Do not perform these examinations in the ED because they may provoke uncontrollable bleeding.
- Perform examinations in the operating room under double set-up conditions (ie, ready for emergent cesarean delivery).
Causes
- Prior uterine insult or injury
- Risk factors
- Prior placenta previa (4-8%)
- First subsequent pregnancy following a cesarean delivery
- Multiparity (5% in grand multiparous patients)
- Advanced maternal age
- Multiple gestations
- Prior induced abortion
- Smoking
Differential Diagnoses
Abruptio Placentae
Disseminated Intravascular Coagulation
Pregnancy, Delivery
Other Problems to Be Considered
Vasa previa
Infection
Vaginal bleeding
Lower genital tract lesions
Bloody show
Workup
Laboratory Studies
The following studies are indicated in placenta previa:
- Beta-human chorionic gonadotropin (beta-hCG) subunit
- Rh compatibility
- Fibrin split products (FSP) and fibrinogen levels
- Prothrombin time (PT)/activated partial thromboplastin time (aPTT)
- Type and hold for at least 4 units
- CBC count
- Apt test to determine fetal origin of blood (as in the case of vasa previa)
- Wright stain applied to a slide smear of vaginal blood, looking for nucleated RBCs, not adult blood
- Lecithin/sphingomyelin (L/S) ratio for fetal maturity, if needed
Imaging Studies
- Transabdominal ultrasonography
- A simple, precise, and safe method to visualize the placenta, this ultrasonography has an accuracy of 93-98%.
- False-positive results can occur secondary to focal uterine contractions or bladder distention.
- Transvaginal ultrasonography
- Recent studies have shown that the transvaginal method is safer and more accurate than the transabdominal method. Transvaginal ultrasonography is also considered more accurate than transabdominal ultrasonography. In one study, 26% of placental localization diagnosed by transabdominal ultrasonography was later changed using transvaginal ultrasonography.
- The angle between the transvaginal probe and the cervical canal is such that the probe does not enter the cervical canal. Some advocate insertion of the probe no more than 3 cm for visualization of the placenta.
- Transperineal ultrasonography: Transperineal ultrasonography has been suggested as an alternate method, especially when instrumentation of the vaginal canal with a probe is a concern. A recent study suggests that transperineal ultrasonography may compliment transabdominal ultrasonography and help eliminate false-positive results using the transabdominal method alone.
- MRI: MRI has been suggested as a safe and alternate method and may be useful in determining the presence of placenta accreta. A large trial determining the efficacy and safety of the use of MRI during pregnancy has not been performed, and further investigation is required.
Other Tests
- Kleihauer-Betke test, if concerned about fetal-maternal transfusion
- Bedside clot test
Procedures
- If the location of the placenta is unknown and sonography is not available, a double set-up bimanual examination under anesthesia (EUA) may be performed in the operating room.
Treatment
Prehospital Care
- The key to prehospital care of placenta previa is to ensure hemodynamic stability of the patient and transfer to an appropriate facility.
Emergency Department Care
- Because of the potential morbidity and mortality secondary to profuse bleeding, obtain immediate gynecologic consultation, if available. Before gynecologic consultation or transfer, the hemodynamic stability of the patient should be addressed. This includes the establishment of 2 large-bore intravenous access lines with intravenous crystalloids or blood products, as necessary.
- Obtain continuous fetal monitoring, if available.
- If the fetus is preterm and immediate delivery is unnecessary (eg, fetus <37 weeks' gestation and hemorrhage not present), the patient may be treated expectantly on an outpatient basis.
- If the fetus is reasonably mature (ie, >37 weeks' gestation) and the patient is in labor or if severe hemorrhage is present, therapy is directed at the delivery of the fetus. The patient should receive crystalloids and/or blood, and the patient should be transferred to the operating room with double set-up conditions.
- A trial of labor may be considered for anterior marginal previa, including oxytocin (Pitocin) augmentation.
- Guidelines for the diagnosis and management of placenta previa have been established.3,4
Consultations
- Consult an obstetrician.
Medication
The goal of ED treatment in patients with placenta previa should be directed at the hemodynamic stability of the patient. The primary therapeutic agents should be intravenous crystalloids and/or transfusions.
Recent studies are now using prothrombin complex and recombinant factor VII to control hemorrhage associated with obstetric complications and placenta previa.
Corticosteroids
Steroids may be administered after consultation with a gynecologist, if vaginal bleeding is mild and intermittent, if the patient is not in labor, and if gestation is less than 37 weeks.
Betamethasone (Celestone)
Helps promote fetal lung maturity.
Dosing
Adult
Assess dosing after consulting with obstetrician
Pediatric
Not established
Interactions
Effects decrease with coadministration of barbiturates, phenytoin, and rifampin; decreases effect of salicylates and vaccines used for immunization
Contraindications
Documented hypersensitivity; systemic fungal infections
Precautions
Pregnancy
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions
Increases risk of multiple complications, including severe infections; monitor adrenal insufficiency when tapering drug; abrupt discontinuation of glucocorticoids may cause adrenal crisis; hyperglycemia, edema, osteonecrosis, myopathy, peptic ulcer disease, hypokalemia, osteoporosis, euphoria, psychosis, myasthenia gravis, growth suppression, and infections are possible complications of glucocorticoid use
Tocolytics
Some specialists advocate tocolytics to promote the time for expectant management of symptomatic placenta previa. They should only be used after consultation with an obstetrician. A recent study seems to suggest that the use of tocolytics increases the duration of pregnancy and increases the baby's birth weight without causing adverse effects on the mother and the fetus.
Magnesium sulfate
Nutritional supplement in hyperalimentation. Cofactor in enzyme systems involved in neurochemical transmission and muscular excitability. In adults, 60-180 mEq of potassium, 10-30 mEq of magnesium, and 10-40 mmol/L of phosphate per day may be necessary for optimum metabolic response. Discontinue treatment as soon as desired effect is obtained. Repeat doses are dependent on continuing presence of patellar reflex and adequate respiratory function.
Dosing
Adult
Assess dosing after consulting with obstetrician
Pediatric
Not established
Interactions
Concurrent use with nifedipine may cause hypotension and neuromuscular blockade; may increase neuromuscular blockade observed with aminoglycosides and potentiate neuromuscular blockade produced by tubocurarine, vecuronium, and succinylcholine; may increase CNS effects and toxicity of CNS depressants and betamethasone; may increase cardiotoxicity of ritodrine
Contraindications
Documented hypersensitivity; heart block; Addison disease; myocardial damage; severe hepatitis
Precautions
Pregnancy
A - Fetal risk not revealed in controlled studies in humans
Precautions
Magnesium may alter cardiac conduction, leading to heart block in digitalized patients; respiratory rate, deep tendon reflex, and renal function should be monitored when electrolyte is administered parenterally; caution when administering magnesium dose because magnesium may produce significant hypertension or asystole; in overdose, calcium gluconate, 10-20 mL IV of 10% solution, can be administered as antidote for clinically significant hypermagnesemia
Terbutaline (Brethine)
Acts directly on beta2-receptors to relax uterine contractions.
Dosing
Adult
Assess dosing after consulting with obstetrician
Pediatric
Not established
Interactions
Concomitant use with beta-blockers may inhibit bronchodilating, cardiac, and vasodilating effects of beta agonists; concomitant administration of MAOIs with beta sympathomimetics may result in a hypertensive crisis; concurrent administration of oxytocic drugs such as ergonovine with terbutaline may result in severe hypotension
Contraindications
Documented hypersensitivity; tachycardia resulting from cardiac arrhythmias
Precautions
Pregnancy
B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Precautions
Maternal death has occurred through intracellular shunting; terbutaline may decrease serum potassium levels, which can produce adverse cardiovascular effects, decrease is usually transient and may not require supplementation
Follow-up
Further Inpatient Care
- Bed rest in the hospital may be recommended for some women with bleeding caused by placenta previa.
- A select population of women may be eligible for outpatient management.
Deterrence/Prevention
- Patients with placenta previa should decrease activity to avoid rebleeding.
- Pelvic examinations and intercourse should be avoided.
- Some women will bleed and possibly go into labor without any inciting cause.
Complications
- Maternal mortality (rare)
- Rebleeding
- Intrauterine growth retardation (IUGR)
- Congenital anomalies
- Fetal anemia and Rh isoimmunization
Prognosis
- Patients with complete placenta previa tend to have poorer pregnancy outcomes. They tend to deliver more prematurely and may require hysterectomies at the time of delivery.
Patient Education
- For excellent patient education resources, visit eMedicine's Pregnancy and Reproduction Center and Women's Health Center. Also, see eMedicine's patient education articles Pregnancy, Bleeding and Vaginal Bleeding.
Miscellaneous
Medicolegal Pitfalls
- Instruments or fingers should not be placed near the cervix during a vaginal examination because uncontrolled bleeding can result. Do not perform vaginal or rectal examinations in the ED.
Multimedia
Media file 1: Placenta previa.
References
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Milosevic J, Lilic V, Tasic M, Radovic-Janosevic D, Stefanovic M, Antic V. [Placental complications after a previous cesarean section]. Med Pregl. May-Jun 2009;62(5-6):212-6. [Medline].
[Guideline] Royal College of Obstetricians and Gynaecologists (RCOG). Placenta praevia and placenta praevia accreta: diagnosis and management. Oct 2005;[Full Text].
[Guideline] Oppenheimer L. Diagnosis and management of placenta previa. J Obstet Gynaecol Can. Mar 2007;29(3):261-73. [Medline]. [Full Text].
Ananth CV, Smulian JC, Vintzileos AM. The effect of placenta previa on neonatal mortality: a population-based study in the United States, 1989 through 1997. Am J Obstet Gynecol. May 2003;188(5):1299-304. [Medline].
Besinger RE, Moniak CW, Paskiewicz LS, Fisher SG, Tomich PG. The effect of tocolytic use in the management of symptomatic placenta previa. Am J Obstet Gynecol. Jun 1995;172(6):1770-5; discussion 1775-8. [Medline].
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Iyasu S, Saftlas AK, Rowley DL, Koonin LM, Lawson HW, Atrash HK. The epidemiology of placenta previa in the United States, 1979 through 1987. Am J Obstet Gynecol. May 1993;168(5):1424-9. [Medline].
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Keywords
placenta previa, disseminated intravascular coagulopathy, vaginal bleeding, pregnancy complications, obstetric complications, total placenta previa, partial placenta previa, marginal placenta previa, low-lying placenta previa, internal cervical os, abnormal placental implantation, uterine bleeding, treatment, diagnosis
Contributor Information and Disclosures
Author
Patrick Ko, MD, Clinical Assistant Professor, Department of Emergency Medicine, New York University Medical School; Assistant Program Director, Department of Emergency Medicine, North Shore University Hospital
Patrick Ko, MD is a member of the following medical societies: American College of Emergency Physicians and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.
Coauthor(s)
Young Yoon, MD, Associate Director, Assistant Professor, Department of Emergency Medicine, Mount Sinai Medical Center
Young Yoon, MD is a member of the following medical societies: Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.
Medical Editor
Joseph J Sachter, MD, FACEP, Consulting Staff, Department of Emergency Medicine, Muhlenberg Regional Medical Center
Joseph J Sachter, MD, FACEP is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American College of Physician Executives, American Medical Association, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.
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Mark Zwanger, MD, MBA is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, and American Medical Association
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CME Editor
John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center
John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.
Chief Editor
Pamela L Dyne, MD, Professor of Clinical Medicine/Emergency Medicine, David Geffen School of Medicine at UCLA; Attending Physician, Department of Emergency Medicine, Olive View-UCLA Medical Center
Pamela L Dyne, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, and Society for Academic Emergency Medicine
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